Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-08-22
2003-02-18
Zalukaeva, Tatyana (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S328600, C525S293000, C525S350000, C525S279000, C525S382000, C524S504000, C524S555000, C524S560000
Reexamination Certificate
active
06521715
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to polymeric pigment dispersants, more particularly, it relates to graft copolymer pigment dispersants having an acetoacetyl amine pigment anchoring group. These dispersants are easy to prepare and are useful in dispersing a wide variety of pigments.
Polymeric pigment dispersants which are effective for dispersing pigments in organic liquids are known in the art and are used to form pigment dispersions that are used in a variety of solvent borne coating compositions. Nowadays, such pigment dispersions are widely used, for example, in exterior solvent borne paints for automobiles and trucks.
Much of the past activity with polymeric dispersants has been with random copolymers, but these relatively inefficient materials are being replaced by structured pigment dispersants having AB block copolymer or graft structures. The graft copolymer dispersants that have been used in the past are described in, for example, Huybrechts U.S. Pat. No. 5,852,123 issued Dec. 22, 1998. Such graft copolymers include a polymeric backbone and macromonomer side chains grafted onto the backbone and have attached to either the macromonomer or backbone, a polar group known as a pigment anchoring group which is designed to adsorb on the surface of a pigment particle and so attach the copolymer dispersant to the pigment surface. There is still a need to improve the binding or anchoring of these dispersants to the pigment surfaces. Ineffective anchoring of the dispersant to a pigment particle surface is highly undesired, as it allows the pigment particles to come close enough together to flocculate and leads to pigment dispersions and ultimately paints of poor stability and rheology and reduced color strength.
Nowadays, many of the modern pigments are chemically or physically treated to incorporate functional groups on their surfaces to enhance their performance. This presents the possibility for enhancing the binding force of a polymeric dispersant to the pigment surfaces, since these functional groups can then become potential sites for anchoring the dispersant polymers onto their surfaces for improved dispersion stability and rheology. The commonly used surface treating agents are pigment derivatives having acidic groups such as sulfonates and carboxylates. Naturally, a dispersant polymer with basic amino groups will be able to have a stronger binding force through the acid-base interaction with these acidic groups and become more effective.
There are several direct and indirect methods for introducing the basic amine functional groups into a dispersant polymer. Yet, they all suffer from certain significant drawbacks. For example, amine containing monomers can be directly copolymerized into the dispersant polymer during the synthesis. However, the commercially available amine containing monomers are few. The amine groups can also be introduced by reacting an amine compound with the epoxide groups that are built into a polymer through a monomer like glycidyl methacrylate. However, only the secondary amines can be cleanly reacted with the epoxide groups without crosslinking/gelling the polymers. The choice is also limited.
Therefore, there is still a need for new chemistries and convenient methods to broaden the choices of the types of amine groups in order to optimize the performance of the pigment dispersants described above.
SUMMARY OF THE INVENTION
The present invention provides a composition suitable for use as a pigment dispersant, which comprises a graft copolymer, preferably an acrylic graft copolymer, wherein the graft copolymer has a weight average molecular weight of about 3,000-100,000 and comprises about 10-90% by weight of a polymeric backbone and correspondingly about 90-10% by weight of macromonomer side chains attached to the backbone wherein
(1) the polymeric backbone is formed from polymerized ethylenically unsaturated monomers and
(2) the side chains are macromonomers that are attached to the backbone at a single terminal point and formed from polymerized ethylenically unsaturated monomers and have a weight average molecular weight of about 1,000-30,000;
wherein the graft copolymer contains about 2 to 70% by weight, based on the total weight of the graft copolymer, of polymerized ethylenically unsaturated monomers containing functional acetoacetate groups that are polymerized into the backbone, the side chains or both, wherein the acetoacetate groups of the copolymer are reacted with a compound bearing a primary amine group to form an acetoacetyl amine pigment anchoring group on the graft copolymer.
The present invention also provides stable and non-flocculating pigment dispersions formed by combining the pigment dispersant of this invention with any number of commercially available pigments and an appropriate organic liquid carrier. These dispersions are particularly useful in solvent borne coatings, especially automotive paints, where they impart uniform color to the paint and, at the same time, provide improved efficiency of pigment use, lower paint viscosity, and reduced emission of volatile organic solvents.
DETAILED DESCRIPTION OF THE INVENTION
The novel pigment dispersant of this invention comprises a graft copolymer formed by the copolymerization of ethylenically unsaturated backbone monomers in the presence of a macromonomer. The macromonomer, which has only one terminal ethylenically unsaturated group, forms the side chains of the graft copolymer and is prepared first. It is then copolymerized with ethylenically unsaturated monomers chosen for the backbone composition to form the graft structure.
The graft copolymer contains about 10-90% by weight, preferably about 20-80% by weight, of polymeric backbone and correspondingly about 90-10% by weight, preferably about 80-20% by weight, of side chains. The graft copolymer has a weight average molecular weight of about 3,000-100,000 and preferably about 10,000-40,000. The side chains of the graft copolymer are formed from macromonomers that have a weight average molecular weight of about 1,000-30,000, and preferably about 2,000 to 15,000. All molecular weights referred herein are determined by GPC (gel permeation chromatography) using a polymethyl methacrylate standard.
The macromonomer useful in the present invention contains only one terminal ethylenically unsaturated group which is polymerized into the backbone of the graft copolymer. The preferred macromonomer is formed from polymerized acrylic monomers and in particular primarily from polymerized monomers of methacrylic acid, its esters, or mixtures of these monomers. Preferred monomers include methacrylic acid, alkyl methacrylates, cycloaliphatic methacrylates, and aryl methacrylates. Typical alkyl methacrylates that can be used have 1-18 carbon atoms in the alkyl group such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, 2-ethyl hexyl methacrylate, nonyl methacrylate, lauryl methacrylate, stearyl methacrylate, 2-(2-methoxyethoxy)ethyl methacrylate, ethoxytriethyleneglycol methacrylate, and the like. Cycloaliphatic methacrylates also can be used such as trimethylcyclohexyl methacrylate, t-butyl cyclohexyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, and the like. Aryl methacrylates also can be used such as benzyl methacrylate, phenyl methacrylate, and the like.
Other ethylenically unsaturated monomers can also be used for forming the macromonomer such as acrylic acid, alkyl acrylates, cycloaliphatic acrylates, and aryl acrylates can be used. Preferred alkyl acrylates have 1-18 carbon atoms in the alkyl group such as methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, 2-ethyl hexyl acrylate, nonyl acrylate, lauryl acrylate, 2-(2-methoxyethoxy)ethyl acrylate, 2-(2-ethoxyethoxy)ethyl acrylate, and the like. Cycloaliphatic acrylates can be used such as cyclohexylacrylate, trimethylcyclohexylacry
Benjamin Steven C.
E. I. du Pont de Nemours and Company
Zalukaeva Tatyana
LandOfFree
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